Mr. Whittaker, who was born to British parents in colonial Kenya, sold an estimated 50 million albums worldwide, becoming a staple of easy-listening charts while cultivating a sunny and often sentimental folk-pop sound. Although he was considered a one-hit wonder in the United States, where his song “The Last Farewell” peaked at No. 19 in 1975, he had a devoted fan base across Europe and especially in Germany, where he toured regularly and released songs in German — recorded phonetically, he said, because he couldn’t speak the language.

A self-described “wandering minstrel” with a well-trimmed beard and wire-rimmed glasses, Mr. Whittaker performed country standards, calypso songs, Scottish ballads, South African dance music and Broadway show tunes, along with compositions that showcased his birdlike whistling and alpine yodeling. Critics praised his showmanship even as they often scoffed at his music, calling it bland and melodramatic.

Reviewing a 1981 concert at Constitution Hall, The Washington Post’s Harry Sumrall wrote that Mr. Whittaker’s brand of pop “bordered on the banal” at times, “one step above Muzak and one below a Mitch Miller singalong.” He went on to call Mr. Whittaker “an entertainer of the first order,” praising his “remarkably clean and refined vocal style” and “uncanny skill” as a whistler.

“At times, he may have seemed behind the times,” Sumrall added, “but at others, he was timeless.”

Mr. Whittaker first drew attention in Britain with the release of his 1969 single “Durham Town (The Leavin’),” which opened with a wistful flute solo, closed with a string of valedictory “la la las” and featured some questionable geography, referencing “the banks of the River Tyne” even though Durham is located on the Wear. To Mr. Whittaker, it initially seemed to have all the makings of a dud.

“I just didn’t have any faith in that song at all,” he recalled on his website. “Far from promoting the single in Britain, I went off to Finland for a cabaret season and television appearances.”

Yet the track became his first Top 20 hit in Britain, peaking at No. 12, above songs by Tom Jones, the Beatles and Fleetwood Mac. Mr. Whittaker went on to find additional success with hits including “New World in the Morning,” the antiwar anthem “I Don’t Believe in If Anymore” and a duet version of “The Skye Boat Song,” with comedian Des O’Connor.

He also scored a belated U.S. hit with “The Last Farewell,” which climbed the Billboard Hot 100 four years after its release in 1971, following its rediscovery by an Atlanta radio programmer. (According to Mr. Whittaker, the programmer’s wife heard the track while on vacation in Canada and persuaded her husband to put it on the air.) Its lyrics, about a sailor bidding goodbye to his lover before boarding a man-of-war bound for England, were written not by Mr. Whittaker but by a British silversmith who responded to a radio contest in which Mr. Whittaker invited listeners to send in verses, with the best put to music.

The song was covered by Elvis Presley, much to the delight of Mr. Whittaker, who often performed a version of “Hound Dog.” Interviewed by Britain’s Express newspaper in 2014, he recalled how Presley’s “drummer told me that, when they were preparing to record anything, Elvis would play my version of ‘The Last Farewell’ about 20 times over to people in the studio, and he’d say, ‘And that’s how we should make records.’ ”

The younger of two children, Roger Henry Brough Whittaker was born in Nairobi on March 22, 1936. His father, a grocer, moved to Kenya from Staffordshire, England, after he was injured in a motorcycle crash and sought a warmer climate for his recovery. His mother was a schoolteacher.

In 1989, a gang of burglars broke into his parents’ home in Nairobi, torturing his mother and killing his 84-year-old father. “It will affect me for the rest of my life,” Mr. Whittaker later said, “but I believe we should all live without hate if we can.”

Growing up, Mr. Whittaker played the guitar and sang in the choir at the Prince of Wales School, now known as the Nairobi School. In his telling, he “was stupid, selfish and angry” before he joined the army for his mandatory national service, spending two years with the Kenya Regiment during its fight against East African rebels known as the Mau Mau.

The experience also pushed him toward music.

“Stuck in the bush camps for months on end meant we had to make our own entertainment,” he said. “Before I knew it, I was standing on a makeshift stage, guitar in hand, having enormous fun developing into a second Elvis.”

Mr. Whittaker later spent 18 months at the University of Cape Town in South Africa, studying for a medical career before dropping out to become a teacher. To burnish his teaching qualifications, he enrolled at University College of North Wales (now Bangor University) in 1959, taking classes in zoology, biochemistry and marine biology.

A tune he wrote for a student concert made its way to a British music publisher, leading to the release of his first single, “The Charge of the Light Brigade,” in 1962. The song flopped — Mr. Whittaker later lamented that he had “tried to sing like Mario Lanza,” the operatic tenor — but later that year he released a version of Jimmy Dean’s “Steel Men,” which rose up the charts just as he earned his degree.

Its success led him to trade teaching for music, kicking off a years-long period in which he apprenticed at pubs in northeastern England, trying to entertain miners as they knocked back pints after work. By 1967, his fortunes were beginning to change, as he helped England win the Knokke song contest in Belgium with his performances of “Mexican Whistler,” which featured his signature warble, and “If I Were a Rich Man,” from the musical “Fiddler on the Roof.”

After the success of “The Last Farewell,” Mr. Whittaker participated in another songwriting contest that resulted in the 1980 track “I Am But a Small Voice,” with lyrics by a 13-year-old girl from the Philippines. Proceeds from the song financed a UNESCO education program for children with disabilities.

Two years later, he became the first singer to release a version of the ballad “Wind Beneath My Wings,” by songwriters Jeff Silbar and Larry Henley. He was followed by singers including Sheena Easton, Lee Greenwood, Gladys Knight and Bette Midler, whose 1988 recording, for the soundtrack of the film “Beaches,” went to No. 1 and won two Grammy Awards.

Survivors include his wife of 59 years, the former Natalie O’Brien, who worked as his manager; five children, Emily Kennedy and Lauren, Jessica, Guy and Alexander Whittaker; a sister; 12 grandchildren; and two great-grandchildren.

Mr. Whittaker seldom returned to East Africa in adulthood, aside from a pilgrimage in the early 1980s to film a television special, “Roger Whittaker in Kenya.” He lived in England and Ireland, where he restored a 10,000-square-foot mansion and overhauled a 17th-century convent, before moving to France in 2012 and announcing his retirement.

There was no returning to the stage, although at age 78 he told the Express that he had “written 18 new songs for an album — and I still whistle very well.”